An electrolyzer is an electrochemical device that can split water into hydrogen and oxygen using electrical power. The typical structure of an electrolyzer cell includes the membrane-electrode-assembly (MEA) for the electrochemical reactions, gas diffusion layers (GDL) to transport oxygen and hydrogen away from the electrode, and additional necessary hardware. A practical electrolyzer includes multiple cells for sufficient hydrogen or oxygen production capability. These cells are connected in series using bipolar separate plates to build a stack with other necessary hardware such as e.g., end plates, cell frame, gaskets, etc. One side of the separate plate faces the hydrogen chamber of one cell, and the other side of the plate faces the oxygen chamber of the adjacent cell (i.e., the plate is bipolar). Depending on the system configuration, large electrolyzer systems could include multiple stacks for high capacity.
Due to the difference in the working conditions in oxygen and hydrogen chambers, the requirements for the GDL and separate plates are different. The common requirement for these components is that they must be electrically conductive. In the oxygen chamber, the GDL and separate plate must have superior resistance to electrochemical corrosion at high electrochemical potentials, typically >1.5 VSHE. On the other hand, in the hydrogen chamber, the GDL and separate plate must have excellent resistance to hydrogen embrittlement, especially for high pressure electrolyzers. The electrochemical corrosion will result in a thick oxide layer on the surface that has high electrical resistance, and reduce the energy efficiency of the electrolyzer. The hydrogen embrittlement will affect the mechanical properties of the plate, resulting the mechanical failure of the stack.
In order to meet these performance requirements, the regular electrolyzer uses two pieces of metal plates to form the bipolar plate. On the oxygen side, a platinum plated titanium plate is used for the high electrochemical potential corrosion resistance. On the hydrogen side, a zirconium plate is used to prevent hydrogen embrittlement. A platinum-plated titanium mesh, screen or porous plate is typically used as the GDL in the oxygen chamber. These components are very expensive.
Therefore, it is desired to use low cost materials to reduce the electrolyzer's cost. Moreover, and specific to the bipolar plates, a one-piece metal plate is resistant to both high electrochemical potential corrosion and hydrogen embrittlement is desired to simplify the stack structure and reduce costs.